First full view of arctic sea ice freeze-thaw cycle highlights sea ice response to climate change

Timing of melting and freezing of the ice surface and bottom of all sites: (a) SMO, (b) SFO, © BMO, and (d) BFO. The color codes (note the different scales for different panels) indicate the respective dates. Gray contours indicate the depth lines of 300 and 2000 m. (e) Variations in dates of melting and freezing onset as a function of latitude. Credit: European Geosciences Union

Years of research show that climate change signals are amplified in the Arctic and that sea ice in this region is sensitive to increasing Arctic warming. Sea ice significantly alters the exchange of heat, momentum and mass between the atmosphere and the ocean. So the timing of sea ice melting and freezing, as well as the length of melting and freezing seasons, play a key role in the “heat budget” of the atmosphere-ice-ocean system.

Until now, most studies calculated the onset of melting and freezing in the Arctic using remote sensing observations from the surface, but rarely examined the freeze-thaw process on the ice floor.

That’s according to a new study published today in the journal European Geosciences Union The cryosphere, an international team of scientists synthesized data from multiple sources from 2001 to 2018 to investigate the spatiotemporal variations of both surface and basal melting/freezing onsets and uncover the mechanism behind it. These findings may improve our understanding of changes in the atmosphere-ice-ocean system and sea ice mass balance in a changing Arctic.

Possible delay in Arctic sea ice loss?

“Thinner ice thickness and thinner snow cover favor earlier onset of basal freezing. The ocean plays a trans-seasonal role in regulating the growth or decay of sea ice,” said lead author Long Lin of the Polar Research Institute of China. .

The researchers found that the overall average basal freezing onset of Arctic multi-year ice was nearly 3 months later than the surface. “Based on synchronous ice and underlying ocean observations, we found the basal freezing lag of the ice relative to the surface, which can be attributed to the regulation of the heat capacity of sea ice itself and the oceanic heat release from the mixed layer and subsurface. low,” says Lin.

According to Lin, even though thinner ice generally experiences a longer freezing season, total ice growth still can’t make up for summer sea ice loss. “From another point of view, the self-regulation of the Arctic sea-ice-ocean system will slow the loss of Arctic sea ice.”

New insights into the beginning of the melting of surface and bottom ice

The study also found that the most significant temporal difference in the onset of melting between the surface and the bottom occurred in the Beaufort Gyre region, where the onset of basal melting occurred more than half a month earlier than the surface. In addition, both multi-year and first-year ice in this region show a trend towards earlier onset of basal melt, which can be attributed to the earlier warming of the ocean surface caused by thinning sea ice thickness and increasing sea ice mobility.

These results provide the first complete picture of the freeze-thaw cycle of Arctic sea ice and its coupling to the atmosphere above and the ocean below. It also highlights the importance of synchronous comprehensive monitoring of the air-ice-ocean system, which helps explain the physical nature of the coupling process.

The researchers call for more intensive and comprehensive observations of the ice mass balance of different ice types and simultaneous observations of upper ocean water properties in the future. This, they hope, will vastly improve our ability to fully understand the Arctic ice-ocean system.

More information:
Long Lin et al, Changes in the Annual Cycle of Sea Ice Freezing and Thawing in the Arctic Ocean from 2001 to 2018, The cryosphere (2022). DOI: 10.5194/tc-16-4779-2022

Provided by European Geosciences Union

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